Bug Description

Following the RAID test case from the ISO tracker; installs fine, boots normally with both disks, boots fine with second disk disconnected, rebuilds array manually when second disk reconnected but grub won't boot with just the second disk in the array attached.

I had a look at this today. I only got as far as setting up test environments before getting distracted by other things, but my preliminary result is that I don't seem to be able to reproduce this immediately in precise, so it may be that we've actually fixed this and I didn't notice! I'll try to verify this more carefully after the Easter weekend.

I've isolated the fix to 1.99-20ubuntu1 by bisection, using KVM snapshots to restore to a known state before each attempt. 1.99-18ubuntu1 failed in the way described in this bug, but 1.99-20ubuntu1 boots successfully from either disk. (As previously noted, the current version in precise, 1.99-21ubuntu2, also succeeds.)

Although I hadn't been expecting it to fix this particular bug - my intention was to improve 4K sector support - this was almost certainly a consequence of "Support non-512B sectors and agglomerate reads", backported from upstream in 1.99-19. That makes a degree of sense since it's quite possible that the pattern of reads caused by using a degraded RAID array tickled earlier bugs in GRUB's disk cache layer.